1. Field of the Invention
This invention relates to a control processor for control-processing a controlled apparatus upon execution of a program.
2. Discussion of the Related Art
In conventional control processors such as programmable logic controllers, a control process consisting of a program execution process, an input and output process and a peripheral service process is repeatedly executed at a high speed after an initial process to control an operation of a controlled apparatus. Upon receiving an operation change instruction from a tool terminal connected to the control processor during control processing, the processor immediately executes a program change process at a timing of the peripheral service process to first execute a prior process of the operation after the program change process and to re-execute the control process in accordance with the program execution.
The conventional control processor, however, has the disadvantages that such program change process takes a fairly long time in comparison with the scan time and an operator inputs a program change command at a random timing by way of a tool terminal to provide undesired affection in an operation of the controlled apparatus or its system. In other words, immediately after receiving a program change command at the timing of the peripheral service process, the control processor executes the program change process at the peripheral service process timing, whereby the time for the peripheral service process is immediately prolonged and the scan time itself is also prolonged to fail to immediately control the operation state of the controlled apparatus or the system including the controlled apparatus even if input or control states change, resulting in undesired affection applied to the controlled apparatus.